The present invention relates to a process for production of a moulded ceramic and/or metallic body. The basic material is a ductile material comprising one or more ceramic and/or metallic components, such as particles, which are mixed or coated with at least one binder and fed into a pre-heated mould cavity of a moulding tool. The mould cavity of said moulding tool is enveloped by at least two mould parts of which at least one wholly or partly consists of a microporous material with communicating pores, which mould part is pre-heated by supply of warm fluid and after terminated moulding cooled by supply of cold fluid. The invention include in a further aspect a moulded body made according to the procedure.
It has for a long time been known to manufacture moulded bodies using various moulding procedures, such as injection moulding, extrusion, blow moulding or casting. The basic material is usually a ductile material consisting of ceramic or metallic powders or particles and one or more binders, additives and the like. A common procedure in making ceramic or metallic moulded bodies often comprises three steps. The first step is the moulding, whereby the ductile material is shaped in the mould of a moulding tool. A second step implies evaporation of binders, additives etc. included in the ductile material. The procedure is terminated by a particle compression, such as a sintering.
The procedure as above typically starts with a mixing or coating of the ceramic or metallic powder or particles with a binder system comprising for example at least one polymer, such as thermosets and thermoplastics, and one or more additives having lubricating properties, such as waxes and stearates. The binder system can suitably be liquid per se or be in a liquid state, such as a solution or a fuse. The mixture is heated, typically.apprxeq.150.degree. C., to a consistency allowing injection and is thereafter fed, for instance by means of an extruder, into the mould part or parts, normally a mould cavity, of a moulding tool, wherein the binder physically, chemically or thermally is transformed into a solid state, and a moulded body consisting of for instance particles bonded together by the binder is obtained. The moulded body is cooled and released from the moulding tool. Binders and additives included in said moulded body are removed by suitable methods, such as heating, freeze drying or vaporisation, whereby a moulded body substantially bonded by particle bodying is obtained. The binder content is here normally less than 5%. Obtained moulded body can now be sintered using various sintering procedures, including among others dense sintering, liquid phase sintering, solid phase sintering, exogas and endogas sintering, reaction sintering, pressure sintering, vacuum sintering, selected laser sintering, microwave sintering and activated sintering. The three hereby disclosed steps can be performed directly after each other in a linked manufacturing unit or be performed at different occasions and in separate units, whereby each of the various stages of the moulded body can be further treated and/or worked.
It has also for a long time been known to pre-heat a moulding tool at production of metallic and ceramic moulded bodies. Such a pre-heating is normally obtained by heated oil or water circulating in a pipe system. Pre-heating can also be performed by means of for example an electric rod or other electro-heating. It is furthermore known to cool a moulded body after terminated moulding by means of cold water. Microporous mould parts having microporous mould surfaces, which mould parts can be heated and/or cooled through communicating pores have for some time been used in connection with moulding of thermosets and thermoplastics.
Cyclic temperature regulation, of a moulding tool, alternating between a cold state, a heated state and back to a cold state and so on, are demanding reasonable cycle times not possible using said oil and water systems. The problem is known from the manufacturing of thermosets and rubbers, both requiring heated moulds for respective reaction and curing mechanism during the moulding. Regulation in such intervals of the temperature in a metallic or ceramic moulded body with reasonable heating and cooling times is due to conductive heat transport very difficult and has so far been a bar to maximised and rational utilisation of moulding tools. A heated mixture of ceramic or metallic particles, binders, additives etc. is when fed into a cold, a comparatively cold or an unevenly heated mould partly cooled and a skin formed on its surface facing the mould. This gives rise to a complexity of undesired side effects, such as inner tension due to differences between surface and core temperature, corrugation due to shear strain changes, uneven particle distribution in the moulded body due to particle piling in parts having reduced temperature. Corrugation can, furthermore, primarily or secondarily cause for instance defects in the surface finish and/or imply difficulties in the production a moulded body of complex geometry. Inner tensions and uneven particle distribution result in moulded bodies and articles having an uneven and/or inferior quality.
The demand for a more even heating of the mould surface(s) of a moulding tool and a more rapid as well as facilitated cycling between heated and cooled state, which means between pre-heating of for example the mould part(s) and/or surface(s) and cooling of the moulded body, is very pronounced.